5. Hill Hill Roads Roads
Topics As Per Syllabus 5.1
Special Consideration Considerati on in Hill Roads
5.2.1 Alignment of Hill Road Design: General Consideration, Route ocation in Hills, Gradient, Design and !"pes of Hair #in $ends, Di%erent !"pes of Hill Road Cross§ions
Special Structures in Hill Roads
1. Introduction • A +ill road is usuall" dened on t+e )asis of terrain. • As per -RS t+e cross slope ma" )e classied as:
• Road +ic+ passes t+roug+ it+ a cross slope of 25/ or more i.e. mountainous or steep is termed as 0Hill Road. • Hill road&one +ic+ passes t+roug+ terrain it+ cross slope of 25/ or more. • !+ere are sections along +ill road it+ cross slope less t+an 25/, esp. +en t+e road follos ri(er route. • It is t+e o(erall terrain t+at must )e considered.
Why Hill Road in Nepal? • -epal area 134,444 s. 6m appro7. • 88/ co(ered it+ t+inl"9sparsel" populated +ills, mountains. • 4/ population reside in +ill" areas and depends on agro products. • ;atera"s, raila"s, aira"s & di7tremes of Climatic Conditions, Diconom", Social Reasons = ustif" t+e Construction of Hill Roads in t+e Hill" Regions.
;+ere !unnels, ?iaduct = #ossi)le )ut -ot >conomical
5. Special !onsideration in Hill Roads
5..1 "esi#n and !onstruction Proble$s o% Hill Roads • C+aracteri*ed )" a +ig+l" )ro6en relief it+ idel" di%ering ele(ations and steep slopes, deep gorges and se(eral atercourses E unnecessaril" increase in road lengt+ • Comple7 geolog" & di%erent roc6 )ed& geolog" di%ers from place to place = assessment for road foundation is not eas" • >n(ironmental impact & remo(al of (egetation etc. & sta)le slope ma" c+ange to unsta)le slope after road construction • Great ?ariation in +"drological condition Fground ater condition (ar" from place to place = ma" lead to damages after road construction • -e eart+ ll for road em)an6ment ma" o(erload t+e relati(el" ea6 underl"ing soil la"er on +ill slope = ma" trigger ne and recurrent slides
• Reuires installation of (arious t"pes of special &arious road structures ' cost ma" rise upto 54 & 84/ of total construction • Steep slopes = +ig+ speed of surface runo% & pro(ision of erosion protection or6s • Construction along relati(el" small approac+ di%erent construction tec+nolog" ma" )e needed
• -eed of special safet" precaution during construction • ?ariations of climatic conditions & precipitation Frain and sno , (elocit" of ind etc. & need considerations • @reuent )lasting • Design of +airpin )ends to get +eig+ts
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Special !onsideration in Hill Roads
1. Selection of Road Alignment 2. Special Geometric Standards BGradient and Hari #in $ends '. Cross§ion Design 3. Design of Drainage Structures BSpecial Structures ma" Reuire 5. Sta)ilit" of Slopes
1. Selection o% Road Ali#n$ent • Alignment t+roug+ +ill" areas is slig+tl" di%erent from aligning t+roug+ a at terrain. • @or t+e purpose of e7cessi(e cutting and lling for road constructions gi(e a" to steepening of slopes +ic+ in turn ill a%ect t+e sta)ilit".
*actors A+ectin# Selection o% Ali#n$ent in ,ountainous and Hilly Areas • @olloing points to )e considered +ile aligning t+e +ill roads:
i- Te$perature •) !+e temperature of air (aries in(ersel" it+ altitude. •) !+e temperature drop )eing a)out 4.5 4C per 144m of rise. •) Similarl", t+e amount of +eat recei(ed )" +ill slopes (aries enormousl" it+ t+eir orientation in relation to t+e e7posure to sun. •) !emperature & loer temperature in +ill = drop )" 4.5 4C per 144m rise & slopes facing sout+ and nort+
ii- Rain%all •) !+e amount of rainfall in +ill" region is in(ersel" proportional to t+e altitude. •) In +ill" regions, ind often os along t+e (alle" and gorges, as conseuence of +ic+ t+e rainfall in t+e (alle" is su)stantiall" +ig+er t+an on +ig+&lands and ater&s+eds. •) Also, ma7imum rainfall occurs in fe mont+s onl". So t+ese all une(en situation create t+e pro)lem in construction and maintenance of t+e road. •) Rainfall& +ea(" rainfall a%ects construction and maintenance
iii- At$ospheric pressure and Winds • Atmosp+eric pressure is in(ersel" proportional to altitude. • At +ig+ altitudes, t+e (elocit" of ind is freuentl" coming at 25 = '4 m9s. • !+e c+ange in c+aracter of ind is due to apprecia)le di%erence of atmosp+eric pressure in (alle"s and on mountain passes. • ;ind&+ig+ ind (elocit" contri)ute to damage =eat+ering of roc6s, )loing aa" )inding material in (alle"
i&- (eolo#ical condition • !+e tendenc" of sedimentar" roc6s is to slip under t+e inuence of force parallel to t+e la"er. • !+e degree of sta)ilit" of +ill slopes depends upon t+e t"pe of roc6, t+e degree of strata inclination or dip, t+e occurrence of cla" seem, t+e +ardness of roc6 and presence of ground ater. • !+e insta)ilit" of road ma" )e due to ground ater, landslides and unsta)le folds.
&- Route location •) !+e approac+ to t+e location of +ill road alignment (aries for t+e sections along t+e (alle" )ottom and along t+e mountain pass. •) !+e rst is called Kri(er routeL and second is called Kridge routeL.
Route ocation • Hill road follo tist and turns& cur(es • ocation of alignment (aries for sections along (alle" and mountain pass • Alignment t+roug+ (alle" & ri(er routeM mountain & ridge route • A +ill road ma" )e onl" ri(er route, ridge route or com)ination of )ot+
Ri&er Route situated • Ser(es rural settlement ne7t to t+e ater course • o (e+icle operation cost
Rid#e Route • Steep gradient, s+arp cur(es including +air pin )ends •
• A(aila)ilit" of material and ater
>7pensi(e roc6 or6s, successi(e mountain pass
Route clim)s up continuousl" from t+e (alle" till mountain pass and descends don
• In(ol(es numerous +ori*ontal cur(es, construction of large • Construction of special structures, tunnels, sno fences etc. )ridges • Special retaining protection on +ill sides • Ri(er training or6s ma" e7tensi(e& toe cutting, etc.
Are most sta)le
a- Ri&er Route • !+e location of a route along t+e ri(er (alle" is 6non as ri(er route. Ri(er route is freuentl" used in +ill road due to comparati(el" gentle gradient. - It is ad(antageous t+at a(aila)ilit" of ater and ot+er construction material in (icinit". - Hoe(er, a ri(er route ma" in(ol(e numerous +ori*ontal cur(es, construction of large )ridges o(er tri)utaries and on stretc+es along steepl" sloping +ill sides.
& It ma" also )e necessar" to construct special structures on +ill side for t+e safe of road against landslides.
b- Rid#e Route • A ridge route is c+aracteri*ed )" (er" steep gradient, numerous s+arp cur(es including +air pin )ends and t+e e7pensi(e roc6 or6s.
& !+e road usuall" follos t+e top section of t+e +ill s"stem and crosses successi(el" mountain pass. & Geologicall" sta)le and comparati(el" mild slope sections are selected for t+e articial de(elopment of t+e route.